The invention generally relates to a fully transposed composite superconductor having an at least approximately rectangular cross section. Preferably, it relates to one which contains a number of conductor elements which are combined in the form of a transposed conductor, and which each have
an at least approximately rectangular cross section with a width B,
at least one conductor core composed of a high Tc superconductor material in a matrix and/or sheath composed of normally conductive material, as well as
with respect to lateral bending in the plane of the width B, a predetermined bending radius and a predetermined bending zone length.
The invention also generally relates to an apparatus for production of this composite superconductor, and for its use.
A composite superconductor is disclosed in xe2x80x9cIEEE Transactions on Applied Superconductivityxe2x80x9d, Vol. 9, No. 2, June 1999, pages 111 to 121.
A power application for high Tc superconductors (referred to for short as HTS conductors in the following text), for example in order to produce transformer or machine winding, requires low-loss conductors with alternating current rated values to the kilo-ampere range. However, all that is available at the moment is HTS ribbon conductors with a small cross section and with current carrying capacity values from about 50 to 100 Arms and 77 K in their own magnetic field. Furthermore, these ribbon conductors are mechanically highly sensitive, and their electrical characteristics depend to a major extent on the magnitude and direction of the local magnetic field in which they are located.
For these reasons, it is necessary to construct high-current superconductors, which can be used for technical purposes, from a large number of individual parallel ribbon conductors in the form of so-called composite conductors, for example according to DE 27 36 157 B2, which is based on a ready-for-use configuration that is continuous as possible. For alternating-current applications at industrial frequencies (in general up to 60 Hz), the ribbon conductors, which are referred to as conductor elements or individual conductors in the following text, of such composite conductors must also be insulated from one another and must be systematically transposed or twisted, in order to ensure that the current is distributed uniformly throughout the entire cross section, and hence to ensure that the alternating current losses are low.
Transparent composite conductors with a high alternating-current carrying capacity are in principle known. These may be configured as follows:
as so-called xe2x80x9cconductor barsxe2x80x9d, for example in the form of transposed conductor bars, with conductor elements composed of copper, for example of large alternating current machines.
as so-called xe2x80x9ctwisting conductorsxe2x80x9d with conductor elements composed of copper or transformers or inductors,
as so-called transposed xe2x80x9cflat or round conductorsxe2x80x9d with conductor elements composed of metallic superconductors such as NbTi in Cu (see the cited DE 27 36 157 B2).
It is also known for HTS conductors to be transposed in order to increase the alternating current carrying capacity. Specific design analyses and design information relating to this relate
to a continuous transposition of round or virtually round HTS conductor elements in single or multiple cables (see, for example, the so-called xe2x80x9cRutherford Cablexe2x80x9d in xe2x80x9cIEEE Transactions on Applied Superconductivityxe2x80x9d, Vol. 7, No. 2, June 1997, Pages 958 to 961),
to achieving a continuous transposition effect in power cables by variation of the pitch of twisted HTS conductor elements, which are in the form of ribbons, from on conductor layer to the next conductor layer (so-called xe2x80x9cPitch Adjustmentxe2x80x9d; see WO 96/39705),
so-called xe2x80x9cin-situxe2x80x9d transposition, that is to say the step-by-step transposition during the production of the winding directly on the winding former, for example for a transformer winding (see, for example, xe2x80x9cIEEE Transactions on Applied Superconductivityxe2x80x9d, Vol. 7, No. 2, June 1997, Pages 298 to 301).
The fundamental structure of a fully transposed composite superconductor composed of HTS conductor elements in the form of a transposed conductor bar is disclosed in the initially cited reference from xe2x80x9cIEEE Transactions on Applied Superconductivityxe2x80x9d. The described composite superconductor is in this case composed of conductor elements based on concepts such as those implemented with conductor elements composed of traditional superconductor materials such as NbTi. However, it has been found that only a relatively low current carrying capacity can be achieved for the overall composite conductor with a design such as this.
An object of an embodiment of the present invention is to refine the composite superconductor having the features mentioned initially, such that it has a better current carrying capacity than this prior art. In this case, one aim is to optimally make use of the original current carrying capacity of its individual conductor elements, which are in the form of ribbons, and to minimize the risks resulting from the mechanical sensitivity and the electrical anisotropy of the conductor elements. It is intended to be able to produce the composite superconductor in virtually any desired length.
According to an embodiment of the invention, an object may be achieved by a bending radius R of greater than 100 times the width B and a bending zone length H of greater than 20 times the width B being provided for each of the conductor elements and by providing ways of fixing the conductor elements to one another.
The measures according to an embodiment of the invention are based on the idea that when a composite superconductor is constructed in the manner of a transposed conductor bar from a number of fully transposed HTS ribbon conductors, which are fully insulated from one another, as conductor elements, the necessary bends, on-end bends and flat bends of the conductor elements must not have radii that are less than critical bending radius values. It has been found that the simultaneous choice of the bending radius and of the bending zone length according to an embodiment of the invention as a function of the conductor element width avoids damage to the superconducting conductor cores of the conducting elements during bending in order to form the transposed conductor bar structure, that is to say during the so-called xe2x80x9ctransposition processxe2x80x9d.
In this case, with the choice of the abovementioned two variables according to an embodiment of the invention, the bending radii for the bending which is required for the transposition process can even be complied with without any problems around the flat faces, and are in the order of normal orders of magnitude. Each conductor element can thus then advantageously contribute to major extent additively to the current carrying capacity of the overall composite superconductor. Since the bending zone length H is considerably greater than in the case of a structure which is known from traditional superconductors is based on the cited prior art, this results in relatively loose composite assembly, which necessitates fixing devices for fixing the conductor elements to one another, and hence for fixing the entire composite conductor. These fixing devices can be chosen with regard to further processing of the composite superconductor.
Composite superconductors according to an embodiment of the invention are therefore advantageously distinguished by a high current carrying capacity and the capability for large-scale production, in particular with regard to long conductor lengths.
Advantageous refinements of the composite superconductor according to an embodiment of the invention can be found.
With regard to the risk of current degradation in the composite superconductor according to an embodiment of the invention a bending radius R of at least 150 times the width B and/or a bending zone length H of at least 50 times the width B are/is advantageously provided for the conductor elements.
In principle it is possible to use different conductor elements, for example with and without superconductor material, and/or with different cross sections, for construction of the composite superconductors according to an embodiment of the invention. However, with regard to a uniform current distribution over the entire composite conductor cross section, it is advantageous to provide an assembly formed by conductor elements having the same construction.
Adhesive joints or soldered joints between the conductor elements may be used as the fixing devices for the composite superconductor according to an embodiment of the invention. A binding or braiding is preferably provided, in order to give the composite superconductor sufficient flexibility. In this case, with regard to possible subsequent impregnation with a synthetic resin or with regard to allowing a good coolant supply, the binding or braiding, in particular, be designed to be appropriately transparent or absorbent.
The composite superconductor is advantageously constructed with conductor elements which each have a ratio of their width B to the respective conductor thickness D of between 5 and 40, and preferably of between 10 and 20. Appropriate conductor elements, which are manufactured commercially, are particularly suitable for transposition while maintaining the stated minimum levels.
With regard to reducing the alternating current losses when using composite superconductors according to the invention, they are advantageously constructed with conductor elements of which at least some are electrically insulated from one another.
In consequence, composite superconductors such as these may be used in particular in a power facility which is operated with alternating current, for example in a transformer or in an electrical machine.
For virtually continuous production of a composite superconductor according to the invention, an apparatus is advantageously provided which has means for joining the individual conductor elements from supply spools together, in a pyramid shape, over a bending region and a guide region in a transposition zone, such that the conductor cross-section position remains at least largely constant, for example horizontally, and has a device for transporting the now transposed structure into a take-up spool via a feed unit and a fixing region. The conductor structure is preferably bound or braided in the fixing region. An apparatus such as this advantageously allows the fundamental requirements for HTS transposed conductor production to be satisfied. In particular, it is possible to satisfy the necessity for the very long bending zones, that are typical for HTS, by functional separation and local distribution one behind the other of the steps of xe2x80x9cposition controlxe2x80x9d, xe2x80x9choldingxe2x80x9d, xe2x80x9cbendingxe2x80x9d, xe2x80x9cmovingxe2x80x9d and xe2x80x9cjoining togetherxe2x80x9d or xe2x80x9ccombiningxe2x80x9d.
The supply spools for the apparatus can advantageously be mounted on a rotating disk such that they can rotate.
The conductor elements are advantageously supplied to the transposition zone in the apparatus by use of a rotating slotted guide disk. In this case, the transposition zone may advantageously have stationary guide elements and a transposition channel.